The safety requirement level to be fulfilled determines whether a function of a technical device is categorized as safety-critical or safety-uncritical. The safety requirement level is a term from the field of functional safety and also referred to as safety integration level (SIL). The desired safety requirement level defines the safety-oriented construction principle of the device that needs to be observed so that the risk of a malfunction fulfills the specified requirements.
If a function is categorized as safety-critical, this means, for example, that this function needs to fulfill the requirements of SIL3 or even SIL4. If a function is categorized as safety-uncritical, this means, for example, that it does not have to fulfill a SIL requirement.
In many cases, technical devices in the field of level measurements, pressure measurements or density measurements that fulfill a safety function (e.g., in the sense of SIL) internally consist of two areas. One area is the safety-critical or safety-relevant area that is responsible for the safety function. The other area is a safety-uncritical area that does not influence the safety function.
Depending on the safety level, all hardware and software components that belong to the safety-relevant area of a device not only require much time and effort during the development phase of the device, but also over the entire life cycle thereof. In contrast, software and/or hardware components in the area that is safety-irrelevant usually can be developed and serviced in a much simpler and more cost-efficient fashion.
Components that have a direct influence on the safety function are usually assigned to the safety-relevant area during the planning phase of the device such that these components can be developed in accordance with the safety function requirements. However, this is not absolutely imperative in all instances and can result in unnecessarily high expenditures and costs.